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Biomedical subjects

Stuart L Graham

Publications and source records attributed to Stuart L Graham.

8 recordsLinked to original sources
PubMed2003

Effect of stimulus check size on multifocal visual evoked potentials.

In this study we examined the effects of varying stimulus check size on multifocal visual evoked potential (VEP). We also evaluated the currently used cortical scaling of stimulus segments. The ObjectiVision multifocal objective perimeter stimulates the eye with random check patterns at 56 cortically scaled segments within the visual field extending to a radius of 26 degrees. All cortically scaled segments have equal number of checks, which gradually increase in size from the center to the periphery, proportional to the size of the segment. Stimuli with 9, 16, 25, 36 and 49 checks/segment were tested on 10 eyes belonging to 10 normal subjects. The check size varied inversely with number of checks per segment. VEP was recorded using bipolar occipital cross electrodes (7 min/eye), the amplitude and latency of responses obtained were compared with the check size at different eccentricities. Our findings suggest that the existing setting with 16 checks/segment subtending 26' to 140' from center to periphery, is the most effective amongst all the check sizes. Decreasing the check size prolongs the latency in the central field only. Cortical scaling of segments generates responses of the same order of magnitude throughout the field, but could be improved slightly to enhance the signal from the outer two rings.

Adult↗
PubMed2003

Effect of pupil size on multifocal pattern visual evoked potentials.

The purpose of this study was to investigate the influence of pupil diameter on the amplitude and latency of multifocal visual evoked potentials (mfVEP). The multifocal objective perimeter (Accumap; Objectivision) was used to stimulate the visual field at 56 sites extending to 32 degrees using a pseudo-random pattern stimulus. The mfVEP were recorded using bipolar occipital electrodes, 7 min/eye. Ten normal subjects were recruited from the community and one eye was randomly selected for testing. The mfVEP were recorded at four different pupil diameters (2 mm, 4 mm, 6 mm, 8 mm), obtained by applying tropicamide (0.5%) or pilocarpine (2%) in different dilutions. Appropriate refractive correction was provided to overcome cycloplegia and achieve a visual acuity of 6/7.5 or better. Analysis revealed that at most pupil diameters the normalized full field amplitude did not show significant variation, except at the most miotic pupil diameter (2 mm), where the amplitude became reduced, based on 2-way anova and Tukey's T method. There was, however, significant correlation between latency and pupil area (correlation coefficient: upper field -0.63, lower field -0.76). The results suggest that even in the presence of mydriatics or miotics, the mfVEP test can be used to assess diseases that affect amplitude, provided near correction is used. The interpretation of latency, however, must be made with caution, as a borderline conduction defect with a dilated pupil may appear normal.

Adult↗
PubMed2002

Multifocal objective perimetry in the detection of glaucomatous field loss.

PURPOSE: To test the ability of a new type of multifocal objective perimetry to identify glaucomatous visual field defects. METHODS: A multichannel visual evoked potential was recorded using the ObjectiVision Accumap perimeter. One hundred patients (age, 62.2 +/- 9.8 years, mean MD -6.5 +/- 4.17 dB) with open-angle glaucoma and confirmed glaucomatous visual field defects were tested and compared with the normal database of 100 normal subjects (age, 58.9 +/- 10.7 years). Both eyes were tested, but for determining sensitivity the eye with the lesser field defect was chosen if both qualified. The amplitude and intereye asymmetry coefficient for each zone of the field were calculated. A mean amplitude and multifocal objective perimetry severity index was calculated for each subject. RESULTS: In 95 of 100 (95%) patients with glaucoma Humphrey field defects were correlated with visual evoked potential amplitude reductions identifying a cluster of three or more abnormal zones. In two of five remaining patients with glaucoma the defect was detected on the intereye asymmetry analysis. Topographic location was well correlated with Humphrey fields. Mean amplitude was significantly reduced in 86 of the glaucoma cases (86%). The glaucoma severity index was abnormal in 93 glaucoma cases and showed a correlation with Humphrey MD (r = 0.67 right eyes, 0.69 left eyes). In 37 glaucoma cases with no scotoma by definition in the fellow eye, 22 (59.4%) had an abnormal multifocal objective perimetry, whereas only eight had some other aspect of their Humphrey visual field flagged as abnormal. CONCLUSIONS: Multifocal objective perimetry can assess the visual field and identify glaucomatous visual field defects. It may have the potential for identifying defects earlier than conventional perimetry.

Adult↗
PubMed2002

Factors affecting awareness and knowledge of glaucoma among patients presenting to an urban emergency department.

BACKGROUND: Until advanced, glaucoma is asymptomatic. For early diagnosis to occur, patients may need to be aware of it and seek assessment regularly. People who have risk factors for glaucoma may have a greater awareness of the disease. METHODS: Patients presenting to an urban hospital emergency department were surveyed with a brief questionnaire to assess their knowledge of glaucoma. Data was collected about their gender, age, family history of glaucoma and presence of systemic hypertension, diabetes, Raynaud's phenomenon, migraines and myopia. RESULTS: Women (Odds ratio 2.3; 95% CI 1.4-3.7; P < 0.01), people who were 40 years or older (Odds ratio 2.2; 95% CI 1.1-4.4; P < 0.05) and those who were aware of a family history of glaucoma (Odds ratio 15.7; CI 5.5-45.3; P < 0.01) knew significantly more about the disease than others. People with other risk factors did not demonstrate significantly greater knowledge despite 89% of all participants having had a previous eye examination. CONCLUSION: This information may be useful to predict which patients may know about glaucoma when they present for an eye examination and who should be targeted in public health campaigns.

Adult↗
PubMed2002

Analysis of risk factors that may be associated with progression from ocular hypertension to primary open angle glaucoma.

BACKGROUND: As a multifactorial disease, glaucoma may be associated with pressure-dependent and pressure-independent factors. Ocular hypertension (OHT) may develop into primary open angle glaucoma (POAG) for many patients. Groups with OHT and POAG were compared for pressure-dependent and independent risk factors. A high prevalence of any factor(s) could indicate a contribution to progression from OHT to POAG. METHODS: A sample of patients with POAG (n = 438) and with OHT (n = 301) were selected from those attending a tertiary referral private glaucoma practice, and data were collected regarding age and intraocular pressure at the time of diagnosis, sex, family history of glaucoma, systemic hypertension, diabetes, Raynaud's phenomenon, migraine and myopia. RESULTS: After multivariate analysis, older age at time of diagnosis (chi(2)(5) = 73.89, P < 0.001), myopia (odds ratio [OR] = 1.5, 95% confidence interval [CI] 1.0-2.2; P < 0.05), a family history of glaucoma (OR = 1.6, 95% CI 1.1-2.3; P < 0.01) and a high intraocular pressure (chi(2)(4) = 16.96; P = 0.002) were found to be more prevalent among those with POAG. No other significant differences could be found between the two groups. CONCLUSION: Patients who have OHT may be at higher risk of developing POAG if they also have myopia, a family history of glaucoma or are of older age.

Adult↗
PubMed2002

Familial amyloidotic polyneuropathy presenting with rubeotic glaucoma.

A 78-year-old man with familial amyloidotic polyneuropathy type I (Met30), presented with rubeotic glaucoma 9 months following an uncomplicated vitrectomy for vitreous amyloidosis. There was retinal neovascularization and extensive retinal vascular closure. In the preceding 9 months, episodes of 'uveitis' and high intraocular pressure are thought to be due to amyloid protein released into the aqueous leading to trabecular meshwork obstruction and high intraocular pressures, thus compounding the ocular ischaemia created by amyloid vascular closure. The patient underwent pan-retinal photocoagulation and Molteno implant surgery. The rubeosis regressed and pressure control was gained but sight was lost.

Aged↗
PubMed2002

Comparison of clinical optic disc assessment with tests of early visual field loss.

PURPOSE: Clinical optic disc assessment may identify glaucomatous optic neuropathy prior to a patient developing visual field abnormalities on achromatic automated peri-metry (AAP). Tests targeting axons that are selectively damaged or whose redundancy is low, such as short wavelength automated perimetry (SWAP) and frequency doubling perimetry (FDP), may detect visual field loss before it is seen on AAP. This study investigated whether patients in whom characteristic glaucomatous optic disc damage was present without AAP abnormalities had visual field abnormalities with SWAP and FDP. METHODS: A sample of patients (n = 50) with ocular hypertension (normal AAP) were selected, who had SWAP, FDP and stereofundus photography performed. The photographs were then analysed by two glaucoma subspecialists who were masked to the assessments of the other and to the patients' SWAP and FDP results. A categorization of the optic discs was made as either normal or abnormal and this was compared with their SWAP and FDP findings. RESULTS: On comparing SWAP and FDP with clinical optic disc assessment as the 'gold standard', the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 33%, 92%, 57% and 81%, respectively, for SWAP and 25%, 89%, 49% and 79%, respectively, for FDP. CONCLUSION: In glaucoma suspects, the study suggests that SWAP and FDP identify subjects with early glaucomatous optic neuropathy missed by AAP.

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